ASMCMD> lsdg -cgH dgroup1

      2  MOUNTED  EXTERN  N         512   4096  1048576      3057     1817                0            1817              0  DGROUP1/
      1  MOUNTED  EXTERN  N         512   4096  1048576      3057     1817                0            1817              0  DGROUP1/

SQL>  select group_number,name,FAILGROUP,REDUNDANCY from v$asm_disk;

GROUP_NUMBER NAME                           FAILGROUP
------------ ------------------------------ ------------------------------
REDUNDA
-------
           0
UNKNOWN

           1 DGROUP1_0000                   DGROUP1_0000
UNKNOWN

           1 DGROUP1_0001                   DGROUP1_0001
UNKNOWN

GROUP_NUMBER NAME                           FAILGROUP
------------ ------------------------------ ------------------------------
REDUNDA
-------
           1 DGROUP1_0002                   DGROUP1_0002
UNKNOWN

SQL> alter diskgroup dgroup1 add failgroup DGROUP1_0000 disk '/dev/oracleasm/disks/VOL4';
alter diskgroup dgroup1 add failgroup DGROUP1_0000 disk '/dev/oracleasm/disks/VOL4'
*
ERROR at line 1:
ORA-15067: command or option incompatible with diskgroup redundancy

oracle@rac2:~> oerr ora 15067
15067, 00000, "command or option incompatible with diskgroup redundancy"
// *Cause:  An attempt was made to use a feature which is not
//          permitted by the diskgroup's redundancy policy.  Common examples
//          are forcibly dropping a disk from an EXTERNAL REDUNDANCY diskgroup,
//          using the FAILGROUP clauses with an EXTERNAL REDUNDANCY diskgroup,
//          or using invalid template attributes.
// *Action: Omit the option from the command.

如果一开始创建的diskgroup是缺省的external redundancy, 那在以后是不能往failgroup中添加磁盘的.